Lithium secondary battery

Abstract

A negative electrode of a lithium secondary battery has a negative electrode active material including at least one element of silicon and tin. Capacities of the positive electrode and the negative electrode of the lithium secondary battery are set as follows. In a completely charged state of the lithium secondary battery charged by a predetermined charging method, the positive electrode active material and the negative electrode active material are in a first partially charged state, respectively. In a completely discharged state of the lithium secondary battery discharged by a predetermined discharging method, the negative electrode active material is in a second partially charged state.

Description

TECHNICAL FIELD[0001]The present invention relates to a lithium secondary battery having an active material including at least one element of silicon and tin in a negative electrode and being excellent in the charge / discharge cycle characteristics.BACKGROUND ART[0002]Recently, with the development of portable devices such as personal computers and portable telephones, batteries as a power source for such devices have been increasingly demanded. The batteries used for the above-mentioned applications are required to be used at ordinary temperatures as well as to have a large energy density and excellent cycle characteristics.[0003]In order to respond to these requirements, for both positive electrode and negative electrode, active materials having a large capacity density have been newly developed. Above all, elemental substances, alloys, or oxides of silicon (Si) or tin (Sn) that can provide an extremely large capacity density are promising materials as negative active materials.[00...

AI Technical Summary

Benefits of technology

[0008]The present invention provides a lithium secondary battery having an active material including at least one element of silicon and tin in a negative electrode and being excellent in charge / discharge cycle characteristics.

[0009]The lithium secondary battery of the present invention has a positive electrode, a negative electrode and a non-aqueous electrolyte having lithium ion conductivity and being interposed between the positive electrode and the negative electrode. The positive electrode contains positive electrode active material absorbing and releasing lithium ions. The negative electrode contains negative electrode active material including at least one element selected from a group consisting of silicon and tin. Then, in a completely charged state of the lithium secondary battery charged by a predetermined charging method, the positive electrode active material and the negative electrode active material are in a first potentially charged state, respectively. Furthermore, in a completely discharged state of a lithium secondary battery charged by a predetermined discharging method, the negative electrode active material is in a second partially charged state. Thus, by combining the charged states of the positive electrode active material and the negative electrode active material, it is possible to suppress the capacity deterioration associated with the charge / discharge cycle. Thus, a battery is designed by combining the charged state of the positive electrode active material and the charged state of the negative electrode active material, and thereby a lithium secondary battery having excellent charge / discharge cycle characteristics can be provided.

Problems solved by technology

However, in lithium secondary batteries using these negative electrode active materials, sufficient charge / discharge cycle characteristics cannot be obtained.

However, as in Patent document 1, when the lithium reference electrode is provided in the battery in order to control the discharge electric potential of the negative electrode using SiO with respect to the lithium reference electrode, the battery configuration becomes complicated, thus making practicability thereof difficult.

Therefore, even if the discharge end voltage is set so that the discharge end electric potential of the negative electrode becomes 0.6 V or less based on the positive electrode, it is difficult to determine whether or not the discharge end electric potential of the negative electrode is maintained to be 0.6 V or less.

Thus, it is difficult to suppress the capacity deterioration associated with the charge / discharge cycle by measuring a battery voltage so as to detect a charge and discharged state of the negative electrode.Patent document 1: Japanese Patent Unexarmined Publication No.

Images